This application claims the priority of German Patent Application, Ser. No. 101 60 352.5, filed Dec. 8, 2001, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.
The present invention relates, in general, to a cross member, and to a method of making a cross member of a twist-beam axle for a motor vehicle.
A twist-beam axle generally includes a rigid and torsionally flexible cross member which has a longitudinal control arm at each end. The longitudinal control arms support on one end a wheel carrier and are attached at their other end to the vehicle body.
Various approaches have been proposed to make the cross member rigid, on one hand, and sufficiently torsionally flexible, on the other hand. German publication no. DE 44 16 725 A1 discloses a cross member which is made over its entire length of a tubular profile which has a torsion-resistant cross section on both ends and in a central area a torsionally flexible U, V, L, X or similar cross section with at least one double-walled profiled leg. French Pat. No. FR 2,654,987 A1 describes a twist-beam axle having a V-shaped cross member which is welded to the longitudinal control arms via U-shaped transition pieces. German Pat. No. DE 27 40 948 A1 describes a twist-beam axle having a cross member composed of two superimposed shells in contact with one another and welded together. German Pat. No. DE 198 46 399 A1 describes a twist-beam rear axle having a cross member in which a stabilizer in the form of a metal sheet insert is arranged so as to ensure a certain torsional stiffness of the cross member.
However, for a number of reasons, the various proposals are endowed with drawbacks and shortcomings relating for example to manufacturing techniques or to the effect that is hoped to be obtained but may not always be realized.
It would therefore be desirable and advantageous to provide an improved method of making a cross member for a twist-beam axle, which obviates prior art shortcomings and which can be made in an easy and cost-efficient manner while yet being reliable in operation
According to one aspect of the present invention, a method of making a cross member for a twist-beam axle of a motor vehicle, includes the steps of shaping a band-shaped metal blank in a profiling unit in a continuous operation to a V-shaped or U-shaped double-walled hollow section with an outer wall and an inner wall, such that the outer wall of the hollow section extends, at least in an apex area thereof, at a distance to the inner wall of the hollow section, and that confronting longitudinal edges of the hollow section extend in the apex area of the outer wall, joining the confronting longitudinal edges of the hollow section by a longitudinal weld seam, smoothing the longitudinal seam of the welded hollow section, and cutting the welded hollow section to size to form a cross member.
A method according to the present invention for making a cross member of a twist-beam axle is economical and cost-efficient as far as production technique is concerned, and is applicable for making a cross member of steel sheet as well as aluminum sheet or other suitable metallic materials. The cross member made in accordance with the present invention is torsionally flexible and light-weight, while still enhancing the vehicle safety, running behavior and comfort of the motor vehicle. As a consequence of the hollow double section, the material consumption and thus the overall weight is reduced.
According to another feature of the present invention, the wall thickness of the metal blank can be best suited to the desired roll stiffness of a twist-beam axle.
The metal blank may be drawn from a coil for supply to the profiling unit, or may supplied to the profiling unit in the form of a flat plate.
According to another feature of the present invention, the welding operation of the hollow section is implemented fully automatically as is the after-treatment of the longitudinal weld seam, in a line without in-between handling of the involved components.
Suitably, the distance between the outer wall and the inner wall in the apex area is a multiple of a wall thickness of the metal blank. In practice, the distance between the outer wall and the inner wall should be at least 10 mm. This measure benefits the manufacture because welding of the longitudinal seam of the hollow section can then easily be automated. Also, the area enclosed by the hollow section can be best suited to vehicle-specific requirements. In this way, roll stiffness and torsional stiffness of the cross member can be adjusted. The roll stiffness can hereby be determined at a measure typical for the motor vehicle, without increase to the weight of the twist-beam axle.